The present invention relates to a process for automatic filling with products, as well as to a device suitable for carrying out the process.
Whenever tanks are to be filled with defined amounts of a product, it is common practice according to state of the art to weigh the tank when it is empty in order to determine its tare and to subsequently fill it with a defined weight. This is done, for example, by placing the tank on scales and then filling it with the product while it is on the scales. This is also the technique employed for filling gas cylinders. When filling gas cylinders, it is also possible to first determine the tare and to subsequently carry out the filling operation while measuring the internal pressure in the cylinder. Once the desired final pressure has been reached, the cylinder is sealed and the filling procedure is completed. In some cases, the determination of the degree of residual filling--which must be carried out prior to any filling operation--can also be done by means of pressure measurement; this is particularly advisable if the residual gas is a gas like hydrogen, which has a low molecular weight.
With some filling operations, manometric and gravimetric determinations can be conducted in any conceivable combination in order to ascertain the degree of residual filling as well as the amount of gas that is filled in. This is particularly the case with gas mixtures which have highly varied properties in terms of the molecular weight of the gas.
A decisive factor during filling, especially when filling with gas, is that the gas cylinder to be filled must be in a state which is suitable for the storage, transportation and utilization of the gas contained in it. This is particularly relevant from a safety standpoint. Thus, corrosive gases which could damage the cylinder as the result of chemical reactions must not be filled into cylinders whose weight falls below a certain value laid down by safety specifications or into cylinders which are not approved for filling with the gas in question. In less extreme cases, it is sufficient for the cylinder to be filled at a lower pressure which does not give rise to any safety concerns. For this reason, nowadays the cylinders to be filled must undergo inspection by humans when they are filled or checked. For this purpose, the cylinders are placed on scales, their weight is determined and those cylinders whose tare deviates too much from the reference value are sorted out manually. As an alternative, a decision has to be made as to whether it might also be possible to fill the cylinders at a lower pressure in order not to have to completely remove them from circulation.
If the objective is to fully automate a filling process, certain requirements must be met in order to be able to dispense with the use of personnel. In a fully automatic device, it is only permissible to fill those cylinders which have a pre-defined weight and which are capable of receiving a likewise pre-defined filling weight. Precisely in the case of gas cylinders, however, it is not possible to ensure such constant preconditions, so that fluctuations in the tare of the cylinders do occur. This can be caused, for instance, by a residual content or by a reduction in the weight of the empty cylinders as the result of corrosion; here, in turn, the age as well as the number of previous filling operations with highly reactive gases play a role. These parameters, however, can vary considerably from cylinder to cylinder so that even in the case of automatic filling devices, it is first necessary to at least manually sort out the unusable cylinders.